Novel cutaneous effects of combination chemotherapy with BRAF and MEK inhibitors: a report of two cases.

The discovery that some melanoma tumours harbour mutations in the BRAF gene (e.g. V600E) and the subsequent development of specific BRAF inhibitors have greatly improved the treatment of metastatic melanoma. Resistance of tumour cells to BRAF inhibitors is reduced by the addition of an MEK inhibitor; both BRAF and MEK inhibitors have been reported to produce a variety of dermatological toxic effects. Benign naevi often harbour BRAF mutations but few reports exist that document the response of naevus cells to BRAF inhibition. We report sarcoidal-type granulomatous inflammation in two patients with metastatic melanoma undergoing treatment with combination BRAF and MEK inhibitor therapy. This inflammation manifested in one patient as a nonspecific papular eruption; in the other, in association with clinical regression of multiple benign-appearing naevi during the course of therapy. The significance of sarcoidal-type inflammation occurring during treatment of metastatic melanoma with a combination of BRAF and MEK inhibitors is unclear. Its association with the clinical regression of benign-appearing naevi suggests a possible exaggerated inflammatory response to degenerating naevus cells in these lesions.

Whole recombinant yeast vaccine induces antitumor immunity and improves survival in a genetically engineered mouse model of melanoma.

Malignant melanoma is one of the deadliest forms of skin cancer and its incidence is expected to rise over the next two decades. At present, there are no effective therapies for advanced melanoma. We have previously shown that administration of whole recombinant yeast expressing human MART-1 (hMART-IT) induces protective antimelanoma immunity in a B16F10 transplantable mouse model. In this study, we examine the effectiveness of the hMART-IT vaccine in a congenic strain of genetically engineered mouse model of melanoma, which recapitulates both the underlying genetics and the proper tumor microenvironment of naturally occurring melanoma. Subcutaneous administration of hMART-IT induced cytotoxicity against melanoma cells and antigen-specific production of Th1-specific cytokines by splenocytes. Weekly administration of hMART-IT significantly delayed the development of melanoma and prolonged the survival of mice compared with controls. Although histological analysis demonstrated diffuse infiltration of CD4(+) T cells and CD8(+) T cells, no reduction of regulatory T cells was observed, suggesting that hMART-IT cannot prevent immunotolerance in the tumor microenvironment. This study provides a proof of concept that genetically engineered mouse models lend valuable insights into immunotherapeutics being tested in the preclinical setting.

Pattern of cutaneous immunoglobulin G deposition in subacute cutaneous lupus erythematosus is reproduced by infusing purified anti-Ro (SSA) autoantibodies into human skin-grafted mice.

Subacute cutaneous lupus and neonatal lupus are closely associated with the presence of anti-Ro (SSA) autoantibodies, but there is no direct evidence establishing a role for anti-Ro (SSA) in these diseases. After parental injection into mice, IgG from sera containing anti-Ro (SSA) will bind human skin grafted onto the mice. To determine whether the antibody binding is due to anti-Ro (SSA), affinity-purified anti-Ro (SSA) and serum depleted of anti-Ro (SSA) were prepared. After injection into human skin-grafted mice, purified anti-Ro (SSA) antibodies bound an antigen in the human skin graft, while preabsorbing anti-Ro (SSA) serum with Ro (SSA) virtually abolished binding to the human skin graft. Moreover, the pattern of IgG deposition was primarily epidermal and was identical in the human skin-grafted mice injected with purified anti-Ro (SSA) when compared with that found in five patients with subacute lupus (four adults, one neonate). These data directly show that anti-Ro (SSA) antibodies bind to the skin, and support the hypothesis that anti-Ro (SSA) autoantibodies are involved in the disease process that produces subacute cutaneous lupus and neonatal lupus.

Presence of IgE antibodies to staphylococcal exotoxins on the skin of patients with atopic dermatitis. Evidence for a new group of allergens.

In the current study, we investigated whether Staphylococcus aureus grown from affected skin of atopic dermatitis (AD) patients secreted identifiable toxins that could act as allergens to induce IgE-mediated basophil histamine release. The secreted toxins of S. aureus grown from AD patients were identified by ELISA using antibodies specific for staphylococcal enterotoxin (SE) exfoliative toxin (ET), or toxic shock syndrome toxin (TSST-1). S. aureus isolates from 24 of 42 AD patients secreted identifiable toxins with SEA, SEB, and TSST accounting for 92% of the isolates. 32 of 56 AD sera (57%) tested contained significant levels of IgE primarily to SEA, SEB, and/or TSST. In contrast, although SEA, SEB, or TSST secreting S. aureus could be recovered from the skin of psoriasis patients, their sera did not contain IgE antitoxins. Freshly isolated basophils from 10 AD patients released 5-59% of total histamine in response to SEA, SEB, or TSST-1 but only with toxins to which patients had specific IgE. Basophils from eight other AD patients and six normal controls who had no IgE antitoxin failed to demonstrate toxin-induced basophil histamine release. Stripped basophils sensitized with three AD sera containing IgE to toxin released 15-41% of total basophil histamine only when exposed to the relevant toxin, but not to other toxins. Sensitization of basophils with AD sera lacking IgE antitoxin did not result in release of histamine to any of the toxins tested. These data indicate that a subset of patients with AD mount an IgE response to SEs that can be grown from their skin. These toxins may exacerbate AD by activating mast cells, basophils, and/or other Fc epsilon-receptor bearing cells armed with the relevant IgE antitoxin.

Evidence for a streptococcal superantigen-driven process in acute guttate psoriasis.

Recent studies have suggested that T cells play a critical role in the pathogenesis of psoriasis. Guttate psoriasis is a well-defined form of psoriasis frequently associated with streptococcal throat infection. This study tested the hypothesis that T cells in acute guttate psoriasis skin lesions may be activated by streptococcal superantigens. Peripheral blood as well as lesional and perilesional skin biopsies were analyzed for T cell receptor V beta repertoire using monoclonal antibodies against 10 different V beta families. Skin biopsies from all patients with acute guttate psoriasis, but not skin biopsies from patients with acute atopic dermatitis or inflammatory skin lesions induced in normal subjects with sodium lauryl sulfate, demonstrated selective accumulation of V beta 2+ T cells (P < 0.05). The expansion of V beta 2+ T cells occurred in both the CD4+ and the CD8+ T cell subsets. Sequence analysis of T cell receptor beta chain genes of V beta 2-expressing T cells from skin biopsies of patients with guttate psoriasis showed extensive junctional region diversity that is more compatible with a superantigen rather than a conventional (nominal) antigen-driven T cell response. All streptococcal isolates from patients with guttate psoriasis secreted streptococcal pyrogenic exotoxin C, a superantigen known to stimulate marked V beta 2+ T cell expansion. These data support the concept that acute guttate psoriasis is associated with superantigenic stimulation of T cells triggered by streptococcal superantigen(s).

Epidermal HLA-DR and the enhancement of cutaneous reactivity to superantigenic toxins in psoriasis.

Streptococcal and staphylococcal superantigens (SAg's) have been implicated in the pathogenesis of inflammatory skin diseases, but the mechanisms by which these toxins act are unknown. The present study assessed the ability of nanogram quantities of topically applied purified toxic shock syndrome toxin-1 (TSST-1), staphylococcal enterotoxin type B, and streptococcal pyrogenic enterotoxin types A and C to induce inflammatory reactions in clinically uninvolved skin of normal controls and subjects with psoriasis, atopic dermatitis, and lichen planus. These SAg's triggered a significantly greater inflammatory skin response in psoriatics than in normal control subjects or in subjects with atopic dermatitis or lichen planus. Surprisingly, skin biopsies did not exhibit the T-cell receptor Vbeta stimulatory properties predicted for SAg-induced skin reactions. By 6 hours after patch testing with SAg's, TNF-alpha mRNA had increased in the epidermis (but not the dermis) in biopsies from psoriatics, compared with controls. Immunohistochemical studies revealed significantly higher HLA-DR expression in keratinocytes from psoriatics than from controls. However, a mutant TSST-1 protein that fails to bind HLA-DR did not elicit an inflammatory skin reaction. These results indicate that keratinocyte expression of HLA-DR enhances inflammatory skin responses to SAg's. They may also account for previous studies failing to demonstrate selective expansion of T-cell receptor Vbetas in psoriatics colonized with SAg-producing Staphylococcus aureus, and they identify a novel T cell-independent mechanism by which SAg's contribute to the pathogenesis of inflammatory skin diseases.

Ultraviolet light induces binding of antibodies to selected nuclear antigens on cultured human keratinocytes.

Antibodies which bind to different nuclear antigens in tissue sections or in permeabilized cell cultures are useful markers of subsets of connective tissue disease, especially of lupus erythematosus (LE), but whether these antibodies are able to react with these intracellular sequestered antigens in vivo and cause immunologic tissue damage has been a matter of much debate. We report experiments which show that ultraviolet light-irradiated, cultured human keratinocytes bind IgG antibodies from the sera of LE patients with either monospecific anti-SSA/Ro, anti-RNP, or anti-Sm activity, which implies that these antigens have been made accessible on the cell surface by ultraviolet irradiation. Normal human sera or LE patient's sera with anti-double-stranded DNA, anti-single-stranded DNA, or antihistone activity do not bind to the surface of irradiated human keratinocytes. In control experiments, all antisera produced the expected patterns of nuclear and cytoplasmic staining of fixed permeabilized, unirradiated keratinocytes. Careful study of the viability and permeability of irradiated keratinocytes by several techniques showed that this apparent cell membrane expression of extractable nuclear antigens (SSA/Ro, RNP, and Sm) following irradiation was seen on injured keratinocytes whose cell membranes were intact, but not on dead cells. It is particularly significant that all six monospecific anti-SSA/Ro sera bound to irradiated keratinocytes, since this antibody antigen system is highly associated with photosensitive cutaneous LE.

NLRP1 promotes tumor growth by enhancing inflammasome activation and suppressing apoptosis in metastatic melanoma.

Inflammasomes are mediators of inflammation, and constitutively activated NLRP3 inflammasomes have been linked to interleukin-1ß (IL-1ß)-mediated tumorigenesis in human melanoma. Whereas NLRP3 regulation of caspase-1 activation requires the adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD (caspase recruitment domain)), caspase-1 activation by another danger-signaling sensor NLRP1 does not require ASC because NLRP1 contains a C-terminal CARD domain that facilitates direct caspase-1 activation via CARD-CARD interaction. We hypothesized that NLRP1 has additional biological activities besides IL-1ß maturation and investigated its role in melanoma tumorigenesis. NLRP1 expression in melanoma was confirmed by analysis of 216 melanoma tumors and 13 human melanoma cell lines. Unlike monocytic THP-1 cells with prominent nuclear localization of NLRP1, melanoma cells expressed NLRP1 mainly in the cytoplasm. Knocking down NLRP1 revealed a tumor-promoting property of NLRP1 both in vitro and in vivo. Mechanistic studies showed that caspase-1 activity, IL-1ß production, IL-1ß secretion and nuclear factor-kB activity were reduced by knocking down of NLRP1 in human metastatic melanoma cell lines 1205Lu and HS294T, indicating that NLRP1 inflammasomes are active in metastatic melanoma. However, unlike previous reports showing that NLRP1 enhances pyroptosis in macrophages, NLRP1 in melanoma behaved differently in the context of cell death. Knocking down NLRP1 increased caspase-2, -9 and -3/7 activities and promoted apoptosis in human melanoma cells. Immunoprecipitation revealed interaction of NLRP1 with CARD-containing caspase-2 and -9, whereas NLRP3 lacking a CARD motif did not interact with the caspases. Consistent with these findings, NLRP1 activation but not NLRP3 activation reduced caspase-2, -9 and -3/7 activities and provided protection against apoptosis in human melanoma cells, suggesting a suppressive role of NLRP1 in caspase-3/7 activation and apoptosis via interaction with caspase-2 and -9. In summary, we showed that NLRP1 promotes melanoma growth by enhancing inflammasome activation and suppressing apoptotic pathways. Our study demonstrates a tumor-promoting role of NLRP1 in cancer cells.

INTU is essential for oncogenic Hh signaling through regulating primary cilia formation in basal cell carcinoma.

Inturned (INTU), a cilia and planar polarity effector, performs prominent ciliogenic functions during morphogenesis, such as in the skin. INTU is expressed in adult tissues but its role in tissue maintenance is unknown. Here, we report that the expression of the INTU gene is aberrantly elevated in human basal cell carcinoma (BCC), coinciding with increased primary cilia formation and activated hedgehog (Hh) signaling. Disrupting Intu in an oncogenic mutant Smo (SmoM2)-driven BCC mouse model prevented the formation of BCC through suppressing primary cilia formation and Hh signaling, suggesting that Intu performs a permissive role during BCC formation. INTU is essential for intraflagellar transport A complex assembly during ciliogenesis. To further determine whether Intu is directly involved in the activation of Hh signaling downstream of ciliogenesis, we examined the Hh signaling pathway in mouse embryonic fibroblasts, which readily responds to the Hh pathway activation. Depleting Intu blocked Smo agonist-induced Hh pathway activation, whereas the expression of Gli2ΔN, a constitutively active Gli2, restored Hh pathway activation in Intu-deficient cells, suggesting that INTU functions upstream of Gli2 activation. In contrast, overexpressing Intu did not promote ciliogenesis or Hh signaling. Taken together, data obtained from this study suggest that INTU is indispensable during BCC tumorigenesis and that its aberrant upregulation is likely a prerequisite for primary cilia formation during Hh-dependent tumorigenesis.

Complex hydrological controls on wet dune slacks: the importance of local variability.

Dune slacks are a species-rich habitat controlled largely by water chemistry and fluctuations in groundwater. Changes in water chemistry and water table level were analysed in 8 piezometers and 15 ephemeral surface water locations at a large UK dune system over a 12-month period. Total nitrogen concentrations in groundwater varied from 0.27-8.21 mg N L(-1), where dissolved organic nitrogen was dominant at the low nitrogen locations and nitrate was dominant at the high nitrogen locations. Principal components analysis of the water chemistry suggests at least four chemically distinct groundwater signatures. Water levels showed strong temporal heterogeneity. Comparisons of water levels with antecedent rainfall identified a component of year-round groundwater feed and differing seasonal responses overlain by a complex series of lags. In summer, there were lags of four, six and seven months with an additional rapid peaky response to daily rainfall with a one-day lag. In winter, water levels were strongly influenced by exogenous groundwater supply, but again exhibited multiple lags. This study shows that local variations in water chemistry and in hydrological regime can be more complicated than previously thought, with clear implications for optimum management of these high priority habitats for conservation.

Heavy metal and nitrogen concentrations in mosses are declining across Europe whilst some "hotspots" remain in 2010.

In recent decades, naturally growing mosses have been used successfully as biomonitors of atmospheric deposition of heavy metals and nitrogen. Since 1990, the European moss survey has been repeated at five-yearly intervals. In 2010, the lowest concentrations of metals and nitrogen in mosses were generally found in northern Europe, whereas the highest concentrations were observed in (south-)eastern Europe for metals and the central belt for nitrogen. Averaged across Europe, since 1990, the median concentration in mosses has declined the most for lead (77%), followed by vanadium (55%), cadmium (51%), chromium (43%), zinc (34%), nickel (33%), iron (27%), arsenic (21%, since 1995), mercury (14%, since 1995) and copper (11%). Between 2005 and 2010, the decline ranged from 6% for copper to 36% for lead; for nitrogen the decline was 5%. Despite the Europe-wide decline, no changes or increases have been observed between 2005 and 2010 in some (regions of) countries.

Pathomechanisms of photosensitive lupus erythematosus.

This review discusses the mechanisms involved in different photosensitive lupus syndromes: acute cutaneous lupus erythematosus, chronic cutaneous (discoid) lupus erythematosus, subacute cutaneous lupus erythematosus, and neonatal lupus erythematosus. It is proposed that there are three principal determinants of photosensitivity in lupus: 1) susceptibility to UVR-induced release of epidermal and dermal cytokines; 2) susceptibility to UVR-induced release or translocation of sequestered antigens in the epidermis or dermis; and 3) different specific immunologic effector mechanisms, activated by cytokines and directed against discrete epidermal targets. Several characteristics of photosensitive lupus are discussed in detail: autoantibody specificities, autoantigen translocation, induction of epidermal intercellular adhesion molecule-a (ICAM-1), vascular activation, cytokine release and T-cell activation, and clinical phototesting. The role of antibodies to the extractable nuclear antigens Ro and La and the relationship to subacute cutaneous lupus erythematosus (SCLE) and neonatal lupus erythematosus is discussed in detail, and a model of SCLE is proposed.

Cytokine modulation of adhesion molecules in the regulation of immunologic cytotoxicity of epidermal targets.

Immunologic cytotoxicity is an important endpoint of the immune response to tumors, viral infected cells, grafted tissues, and exogenous microorganisms, and is also an important mechanism of disease, especially in autoimmunity. There are multiple mechanisms of immunologic cytotoxicity, but each has three major stages: leukocyte/target attachment, specific recognition, and target lysis following effector activation. Adhesion molecules present on leukocytes and potential targets appear to be involved in all three stages of cytotoxicity. A major factor in all types of cellular cytotoxicity is the interaction of LFA-1 on leukocytes and CAM-1 on targets. Modulation of ICAM-1 levels on target by the cytokines TFN-g, IL-1, and TNF-a is a major point of control of the susceptibility of targets to cytotoxicity by many different cytotoxic mechanisms. It also appears that modulation of the avidity of LFA/ICAM-1 binding is another important control point in modulating immunologic cytotoxicity. Cytokines also have important effects on immunologic cytotoxicity in ways other than adhesion molecule induction: effector priming to better respond to specific recognition signals, effector mobilization into tissue, and expansion of cytotoxic effector populations. ICAM-1 on the surface of epidermal keratinocytes and melanocytes is likely to greatly influence cytotoxic damage of these cells in diseases as photosensitive lupus erythematosus, lichen planus, erythema multiforme, and vitiligo. It has been found that the epidermal staining pattern for ICAM-1 in each of these diseases in distinctive and different in each disease. It is proposed that disease-specific induction of ICAM-1 by factors such as UVR and herpes-virus is an important determinant in triggering these skin diseases and in determining the pattern of disease.

Cytokine-induced ICAM-1 expression in human keratinocytes is highly variable in keratinocyte strains from different donors.

Induction of intercellular adhesion molecule 1 (ICAM-1) expression in the epidermis is felt to be an important initiator of leukocyte/keratinocyte interactions in many inflammatory skin diseases. The purpose of this project was to determine the individual variability of cytokine-induced ICAM-1 expression in human keratinocytes obtained from different donors. In 55 different keratinocyte strains, there was significant individual variability in ICAM-1 expression by either tumor necrosis factor alpha (TNF-alpha) or interferon-gamma. There was no correlation (r = 0.266, p = 0.06) in response of the same strain to either TNF-alpha or interferon-gamma. Multiple (n = 22) keratinocyte strains showed no significant induction of ICAM-1 expression to IL-1. The level of ICAM-1 expression in response to TNF-alpha and ultraviolet radiation (UVR) in individual strains was highly correlated in three different comparisons: level of stimulated response versus baseline (TNF-alpha and UVR both p < 0.0001); stimulation index TNF-alpha versus UVR (p = 0.00947); and variability of stimulated response versus variability of baseline (TNF p < 0.001; UVR p = 0.002). UVR-induced release of TNF from keratinocytes also showed variability among different keratinocyte strains. The UVR-induced ICAM-1 response in human keratinocytes and transformed epithelial cell was variably blocked with anti-TNF antibodies. The release of TNF from keratinocytes by UVR and the individually variable but linked characteristics of UVR and TNF-alpha stimulated ICAM-1 expression support the hypothesis that TNF-alpha is a major mediator of UVR-induced ICAM-1 expression.

Influence of inflammatory mediators and cytokines on human melanocyte function.

The fully differentiated human melanocyte functions as a necessary and integral part of the epidermis, synthesizing melanin in intracellular organelles and transferring these pigment-containing organelles to surrounding keratinocytes. The epidermal environment contains multiple inflammatory mediators, cytokines, and growth factors that may alter constitutive melanocyte function. Constitutive melanocyte function can also be markedly altered by release of such mediators in inflammatory dermatoses. Many of the same factors can also be released by ultraviolet radiation and psoralen+ultraviolet A treatment. These inflammatory mediators and cytokines affect not only melanocyte pigment production, but also proliferation, differentiation, immunologic susceptibility and cytotoxicity, inflammatory mediator, cytokine and matrix protein production, and cell movement. The effect of inflammatory mediators and cytokines on melanocytes and the regulation of these effects are an active area of investigation.

The state of differentiation of cultured human keratinocytes determines the level of intercellular adhesion molecule-1 (ICAM-1) expression induced by gamma interferon.

Inducing the expression of ICAM-1 (CD54) on the surface of epidermal keratinocytes is an important step in initiating leukocyte interaction with the epidermis. We studied the effect of keratinocyte differentiation and of drugs used to treat epidermal inflammation on the induction of this important adhesion molecule. Cell membrane expression of ICAM-1 in cultured human keratinocytes was analyzed using both immunofluorescence and FACS analysis of staining with anti-ICAM-1 monoclonal antibody and was correlated with markers of keratinocyte differentiation. Cell-surface ICAM-1 expression was induced by gamma interferon in all culture conditions, but was significantly greater (p less than 0.014) in cells grown in low-calcium medium ([Ca++] 0.03 mM), and correlated with increased staining for the basal cell keratin K5. The synthetic retinoid Etretin (Ro 10-1670) enhanced the interferon-induced ICAM-1 expression over a wide concentration range (10(-8)-10(-5) M); however, this effect was only seen in the more differentiated cells grown in 0.15 mM and 1.0 mM calcium and not in the cells grown in 0.03 mM calcium. The Etretin effects on intracellular K5 staining paralleled those on cell-surface ICAM-1. Anti-inflammatory glucocorticoids had no effect on ICAM-1 expression in cultured human keratinocytes, even at suboptimal gamma interferon doses (5 U/ml). beta-estradiol, on the other hand, mimicked the Etretin effect, increasing both IFN induction of ICAM-1 expression and K5 staining in more differentiated keratinocytes in 0.15 and 1.0 mM calcium, but not in those in 0.03 mM calcium. Both Etretin and beta-estradiol decreased staining of involucrin, a marker of terminal differentiation, supporting the proposition that in this experimental system these drugs suppress keratinocyte differentiation. The enhanced ICAM-1 induction in keratinocytes with a basal level of differentiation correlates with the in vivo effects of interferon on ICAM-1 and may be a principal determinant in the patterns of ICAM-1 seen in inflammatory skin diseases.

Antibody-dependent cellular cytotoxicity and skin disease.

Antibody dependent cellular cytotoxicity (ADCC) is a recently described mechanism of immunologic lysis in which cellular targets sensitized by specific antibodies are efficiently and selectively lysed by Fc receptor (FcR) bearing nonspecific effectors. Immunoglobulins of various classes (IgG, IgM, IgA, IgE) and various cellular effectors (large granular lymphocytes, monocyte/macrophages, T lymphocytes, neutrophils, and eosinophils) can induce ADCC in vitro, and the importance of ADCC in vivo is being tested experimentally in resistance to viral, bacterial, and parasitic infection, in tumor surveillance, in allograft rejection, and in inflammatory diseases. There is much indirect evidence that ADCC may be the mechanism of damage of different cellular targets in skin diseases, but the best direct evidence concerns immunologic keratinocyte damage, especially in cutaneous lupus erythematosus (LE). We have shown that keratinocytes of several species are highly susceptible to lymphocyte and monocyte-mediated ADCC, but not to neutrophil or eosinophil ADCC in vitro using two different cytotoxicity assays. In contrast, complement was a relatively ineffective mediator of lysis of metabolically intact keratinocyte targets. Patients with certain cutaneous lupus syndromes have serum antibodies capable of inducing monocyte and lymphocyte ADCC of targets coated with extractable nuclear antigens. We have shown that these antigens apparently move to the cell membrane of keratinocytes in vitro following ultraviolet irradiation. In an animal model, we have shown that antibodies to SSA/Ro bind to human keratinocytes in vivo, especially after ultraviolet irradiation. This antigen/antibody system is highly associated with 3 different photosensitive LE syndromes. The experimental linkage of UV radiation to autoantibody binding to keratinocytes and the demonstration of mononuclear cell-mediated ADCC causing keratinocyte lysis support our hypothesis that the keratinocyte damage and mononuclear cell infiltrate seen histologically in cutaneous LE are part of an ADCC process.

The effect of epicutaneous glucocorticosteroids on human monocyte and neutrophil migration in vivo.

The effect of epicutaneous methyl prednisolone (MP) at 10-4, 10-5, and 10-6 molar concentration was studied in 54 normal, healthy volunteers using a new, in vivo microchemotaxis technique. Significant inhibition of monocyte chemotaxis occurred at all concentrations studied and persisted over a 24-hr period with 10-4 molar MP. Neutrophil chemotaxis was significantly inhibited only with 10-4 MP. The inhibitory effect of MP on neutrophil and monocyte chemotaxis occurred earlier and at lower concentrations if the skin sites were pretreated with steroid. Thus, when corticosteroids are applied on abraded skin in concentrations achievable in vivo, monocyte chemotaxis into tissue is inhibited for longer periods and at lower drug concentrations than is neutrophil chemotaxis. By avoiding the significant systemic effects of corticosteroids on circulating monocyte and neutrophil populations, these experiments establish that local inhibition of chemotaxis is an important anti-inflammatory effect of corticosteroids, with differential effect on monocytes and neutrophils.